1. Field of the Invention
The disclosed invention is related in general to the field of fuel pressurization systems for fuel injectors of internal combustion engines, and in particular to high pressure fuel intensifiers and fuel rails.
2. Description of the Related Art
In recent years, the design requirements for internal combustion engines have undergone significant changes, due to the need for improved fuel economy and reduced emissions. For example, fuel injectors employed in such engines, and in particular diesel engines, are sometimes designed to operate at pressures that are an order of magnitude greater than were common in the past. Currently, injection pressures may exceed 25,000-30,000 psi. This increased pressure provides improved injection characteristics such as fuel/air mixing in the cylinder, improved combustion temperature, and shortened injection duty cycles to allow an appropriate volume of fuel to be injected at an optimum point in the respective cylinder stroke.
According to one general method, the fuel for each injector of an engine is pressurized by a respective intensifier piston, generally incorporated into the injector, to boost the pressure of the fuel. In some cases, hydraulic fluid, pressurized to a typical hydraulic operating pressure of around 2,000 to 4,000 psi, is employed to drive the intensifier pistons, and fuel is supplied to the injectors under low pressure by a fuel pump. In other cases the fuel is pre-pressurized to a hydraulic operating pressure and employed to drive the intensifier pistons, as well. This general method is preferred by some because the fuel and hydraulic lines supplying the injectors are not required to operate at the very high injection pressures. However, there are disadvantages with this method as well. For example, the complexity of the injectors makes them more likely to malfunction, and they are expensive to repair or replace.
According to another general method, a high-pressure fuel rail is provided, from which each injector of the engine is supplied. The fuel rail is pressurized by one or more intensifier pistons driven hydraulically, or by a cam coupled mechanically to the engine. Because the rate of fuel flow in the engine is not constant, but is related to engine load and rpm, the intensifier piston must be capable of providing fuel at a rate that at least meets the maximum expected fuel demand of the engine.
Examples of some common rail fuel injection systems are disclosed in the following U.S. patents and published patent applications: U.S. Pat. Nos. 6,497,217; 6,786,205; 6,832,599; 2003/0089332; and 2004/0168673, all of which are incorporated herein by reference, in their entireties.